Beginning in 2015, scientists plan to detect new elementary particles with the LHC | AGÊNCIA FAPESP

Researchers say operation at higher power levels could lead to the discovery of particles not envisioned by current physics (photo: CERN)

Beginning in 2015, scientists plan to detect new elementary particles with the LHC

September 17, 2014

By Elton Alisson

Agência FAPESP – Beginning in 2015, operation of the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) in Switzerland could lead to the discovery of elementary particles not yet observed in experiments and test theories that go beyond the current knowledge of physics.

The assessment was made by researchers taking part in the “Going on After the LHC8 (GOAL) Workshop,” held August 11-15, 2014 at the Institute for Theoretical Physics (IFT) of São Paulo State University (Unesp).

Promoted by the International Center for Theoretical Physics (ICTP) South American Institute for Fundamental Research (ICTP-SAIFR) and supported by FAPESP, the meeting brought together 25 theoretical physicists from Europe, the United States, Brazil and other South American countries.

The event’s goal was to analyze and discuss the data obtained through experiments conducted in the LHC in recent years, when the collider operated at 8 teraelectron volts (TeV) of power, equivalent to 8 trillion electron volts.

Meeting participants also estimated potential discoveries that could be made beginning in 2015, when the intensity of proton beams and energy at the center of mass of the world’s largest particle accelerator will be increased to 13 and 14 TeV.

“Through experiments in the LHC, we intend to identify evidence of a new physics, detecting new elementary particles and testing theoretical ideas beyond the Standard Model [theory developed over the past 50 years that describes the strong, weak and electromagnetic interactions of the basic particles that constitute all matter],” said Mariano Quirós, researcher at the High Energy Physics Institute (Ifae) of the Universitat Autònoma de Barcelona (UAB), to Agência FAPESP.

According to Quirós, Standard Model predictions have been exhaustively tested and proven in recent decades through experimental data such as that obtained from the LHC itself.

The Higgs boson (a subatomic particle postulated in 1964 by British physicist Peter Higgs), detected in the LHC in July 2012, was the last element needed to completely validate the theory.

Quirós said that despite this success, the Standard Model presents flaws that are leading theoretical and experimental physicists to consider the possible existence of a new physics.

“The Standard Model predicts many phenomena and particles but does not point to their origin or answer a series of questions. This is causing us to have a certain amount of pessimism with regard to the theory and leading us to believe that a new physics exists,” he said.

New particles

One of the gaps in the Standard Model, according to physicists, is that it does not predict the existence of particles such as dark matter, which is responsible for nearly 25% of the density of energy in the Universe.

The theory also fails to identify the mass of neutrinos, electrically neutral subatomic particles that weakly interact with others only through gravitational interaction, and it does not consider the significance of the interactions between particles.

“The Standard Model provides us with many more predictions than parameters that we could follow to confirm them,” Quirós stated.

In an effort to try to solve these problems, some theoretical physicists have begun to propose new theories over the past four decades, such as the theory of supersymmetry.

Proposed in the early 1970s, the theory of supersymmetry states that for each boson (responsible for transmitting the forces of nature) there is one corresponding fermion (such as quarks, electrons and neutrinos) that has the same mass and internal quantum number, and vice versa.

If the theory is proven, the number of elementary particles known today would grow significantly. This outcome is a possible result of the operation of the LHC at higher energy beginning in 2015, when the proton beams of the collider are accelerated to more than 99.99999% the speed of light.

“It may be that with the 8 TeV energy at which the collider has operated in recent years, it has not been possible to produce new particles predicted by the supersymmetry theories,” said Eduardo Pontón, researcher at ICTP-SAIFR and one of the event organizers at IFT.

“The increased center-of-mass energy in the LHC could help find these new particles, which may be similar to the Higgs boson. If the existence of these particles is confirmed, the Standard Model can be extended,” Pontón explained.

According to the researcher, the higher power levels of the LHC would also enable more precise measurement of certain phenomena and thus allow the inference of the existence of particles that are not detectable in the collider.

“It’s possible that there are very heavy particles to be directly generated in the LHC but that have an indirect effect on the measurements to be made starting in 2015,” Pontón explained.

“If we conduct these precise measurements, it could be possible to infer the existence of these particles, and this will lead to construction of an accelerator that has much more power than the LHC,” he said.

A group of researchers from the United States, Europe, Japan and China are already discussing the possibility of building a particle accelerator similar to the LHC but with power nearly 10 times higher, at 100 TeV, for example.

Another possibility under discussion is the construction of a collider different from the LHC, designed not for collisions of protons but for collisions of electrons, which, despite having less energy, would allow more precise measurements to be made, Pontón said.

“These two possibilities are being discussed, but nothing has been decided yet. These projects would take a long time and require international cooperation to be conducted,” Pontón said.

Enhancing contact

According to Pontón, the 25 theoretical physicists who participated in the event are among the researchers most active in the field of physics beyond the Standard Model, and many of them, who like Quirós have been at CERN since May, were visiting Brazil for the first time.

Event organizers took advantage of the visit by the foreigners to present the ICTP-SAIFR and opportunities for exchanges between graduate students and researchers, in addition to visiting scientist programs and collaborative research with the particle physics group at the center, made up of Pónton, researcher Rogério Rosenfeld, post-doctoral fellows, and master’s and doctoral students.

“On average, we hold two events every month, including two-week courses and smaller scientific events, such as workshops and mini-courses. And the number of events is growing,” explained Nathan Berkovits, director of the ICTP-SAIFR.



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